1. Field of the Invention
The present invention relates to a method and apparatus for modulating a particular light source used for laser display, and more particularly, to an apparatus and method for converting tunable laser light into a green light source using quasi-phase-matching second-harmonic generation (QPM-SHG) and modulating the laser light into a stable laser display light source using digital modulation.
This work was supported by the IT R&D program of MIC/IITA [2005-S-051, Photonic device integrated module for optical access network]
2. Description of the Related Art
Laser display is expressed by using a method of modulating the outputs of a blue laser, a green laser, and a red laser according to the scan period of a scan mirror. Recently, microminiature and low-power laser displays, which can be easily carried, have become popular. In order to implement these laser displays, tri-color light sources, which are modulated to a level of 20 MHz when video graphics array (VGA) images are displayed, are required. Conventionally, semiconductor lasers have implemented modulation light sources for blue and red. However, it is difficult to directly realize green color using a semiconductor laser.
Processing light output from a wavelength-adjustable semiconductor laser, i.e., a Distributed Bragg Reflector Laser Diode (DBR LD) by using a Quasi-Phase-Matching Second-Harmonic Generation (QPM-SHG) device has been considered in order to implement green color. However, color conversion using the QPM-SHG device is so sensitive to wavelength change that when an output of the DBR-LD is modulated to about 20 MHz, it is difficult to exactly maintain the wavelength of the output. Moreover, it is difficult to adjust green light output to a desired brightness on a screen in analog mode.